Recent studies have identified several amino acid sequences that interact with the ribosomal interior components and arrest their own elongation. Whereas stalling of the inducible class depends on specific low-molecular weight compounds, that of the intrinsic class is released when the nascent chain is transported across or inserted into the membrane. The stalled ribosome alters messenger RNA secondary structure and thereby contributes to regulation of the cis-located target gene expression at different levels. The stalling sequences are divergent but likely to utilize non-uniform nature of the peptide bond formation reactions and are recruited relatively recently to different biological systems, possibly including those to be identified in forthcoming studies. (C) 2010 Elsevier Inc. All rights reserved.